An El Niño in the Pacific Ocean almost always hampers hurricane activity in the Atlantic Ocean–sometimes by as much as 50 percent–a new study shows.

An El Niño occurs when warm waters in the Pacific Ocean influences weather patterns around the world. Researchers considered two distinct types of El Niño: a Central Pacific (also known as “warm pool” El Niño) and East Pacific or “cold tongue” El Niño.

“This happens because the unusual warming of the Pacific Ocean leads to a shift in the typical location of deep convection (intense rainstorms), which in turn impacts high-level winds, causing greater wind shear which leads to unfavorable conditions for storms to develop.

“Very strong El Niño conditions in 2015 contributed to the second most active hurricane season ever recorded in the eastern Pacific Ocean. So while an El Niño can help reduce hurricane impacts in the Atlantic basin, impacts can be much worse over the eastern North Pacific basin.”

Patricola says the findings, published in Nature Geoscience, could help improve seasonal and climate change forecasts.

“Our study gives us a more general understanding of how El Niño and its variations in location and intensity, influence hurricane seasons in both the Atlantic and eastern Pacific,” she points out.

“In essence, we found that strong El Niño events that occur over the warmer locations of the Pacific drive the greatest changes in Western Hemisphere hurricane seasons. These findings can help improve seasonal forecasts, and also show the importance of understanding changes in El Niño locations, intensity and frequency in predicting hurricane activity in the future.”